diff --git a/poetry.lock b/poetry.lock
index d7f9cc4..ccdc88f 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -78,6 +78,20 @@ category = "dev"
 optional = false
 python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
 
+[[package]]
+name = "coverage"
+version = "6.4.1"
+description = "Code coverage measurement for Python"
+category = "dev"
+optional = false
+python-versions = ">=3.7"
+
+[package.dependencies]
+tomli = {version = "*", optional = true, markers = "python_full_version <= \"3.11.0a6\" and extra == \"toml\""}
+
+[package.extras]
+toml = ["tomli"]
+
 [[package]]
 name = "defusedxml"
 version = "0.7.1"
@@ -229,6 +243,35 @@ tomli = ">=1.0.0"
 [package.extras]
 testing = ["argcomplete", "hypothesis (>=3.56)", "mock", "nose", "pygments (>=2.7.2)", "requests", "xmlschema"]
 
+[[package]]
+name = "pytest-asyncio"
+version = "0.18.3"
+description = "Pytest support for asyncio"
+category = "dev"
+optional = false
+python-versions = ">=3.7"
+
+[package.dependencies]
+pytest = ">=6.1.0"
+
+[package.extras]
+testing = ["coverage (==6.2)", "hypothesis (>=5.7.1)", "flaky (>=3.5.0)", "mypy (==0.931)", "pytest-trio (>=0.7.0)"]
+
+[[package]]
+name = "pytest-cov"
+version = "3.0.0"
+description = "Pytest plugin for measuring coverage."
+category = "dev"
+optional = false
+python-versions = ">=3.6"
+
+[package.dependencies]
+coverage = {version = ">=5.2.1", extras = ["toml"]}
+pytest = ">=4.6"
+
+[package.extras]
+testing = ["fields", "hunter", "process-tests", "six", "pytest-xdist", "virtualenv"]
+
 [[package]]
 name = "tomli"
 version = "2.0.1"
@@ -239,7 +282,7 @@ python-versions = ">=3.7"
 
 [[package]]
 name = "typing-extensions"
-version = "4.2.0"
+version = "4.3.0"
 description = "Backported and Experimental Type Hints for Python 3.7+"
 category = "dev"
 optional = false
@@ -260,7 +303,7 @@ multidict = ">=4.0"
 [metadata]
 lock-version = "1.1"
 python-versions = ">=3.9,<4"
-content-hash = "ec537cb22f7488971d12450524aec30918e6d42c6eac78fcd4022fe8293d935a"
+content-hash = "b769a6d3035a1a4da43e3c09098d02510dfb9b45f7e67c6ed6874296d9c634e8"
 
 [metadata.files]
 aiohttp = [
@@ -361,6 +404,49 @@ colorama = [
     {file = "colorama-0.4.5-py2.py3-none-any.whl", hash = "sha256:854bf444933e37f5824ae7bfc1e98d5bce2ebe4160d46b5edf346a89358e99da"},
     {file = "colorama-0.4.5.tar.gz", hash = "sha256:e6c6b4334fc50988a639d9b98aa429a0b57da6e17b9a44f0451f930b6967b7a4"},
 ]
+coverage = [
+    {file = "coverage-6.4.1-cp310-cp310-macosx_10_9_x86_64.whl", hash = "sha256:f1d5aa2703e1dab4ae6cf416eb0095304f49d004c39e9db1d86f57924f43006b"},
+    {file = "coverage-6.4.1-cp310-cp310-macosx_11_0_arm64.whl", hash = "sha256:4ce1b258493cbf8aec43e9b50d89982346b98e9ffdfaae8ae5793bc112fb0068"},
+    {file = "coverage-6.4.1-cp310-cp310-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:83c4e737f60c6936460c5be330d296dd5b48b3963f48634c53b3f7deb0f34ec4"},
+    {file = "coverage-6.4.1-cp310-cp310-manylinux_2_5_i686.manylinux1_i686.manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:84e65ef149028516c6d64461b95a8dbcfce95cfd5b9eb634320596173332ea84"},
+    {file = "coverage-6.4.1-cp310-cp310-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:f69718750eaae75efe506406c490d6fc5a6161d047206cc63ce25527e8a3adad"},
+    {file = "coverage-6.4.1-cp310-cp310-musllinux_1_1_aarch64.whl", hash = "sha256:e57816f8ffe46b1df8f12e1b348f06d164fd5219beba7d9433ba79608ef011cc"},
+    {file = "coverage-6.4.1-cp310-cp310-musllinux_1_1_i686.whl", hash = "sha256:01c5615d13f3dd3aa8543afc069e5319cfa0c7d712f6e04b920431e5c564a749"},
+    {file = "coverage-6.4.1-cp310-cp310-musllinux_1_1_x86_64.whl", hash = "sha256:75ab269400706fab15981fd4bd5080c56bd5cc07c3bccb86aab5e1d5a88dc8f4"},
+    {file = "coverage-6.4.1-cp310-cp310-win32.whl", hash = "sha256:a7f3049243783df2e6cc6deafc49ea123522b59f464831476d3d1448e30d72df"},
+    {file = "coverage-6.4.1-cp310-cp310-win_amd64.whl", hash = "sha256:ee2ddcac99b2d2aec413e36d7a429ae9ebcadf912946b13ffa88e7d4c9b712d6"},
+    {file = "coverage-6.4.1-cp37-cp37m-macosx_10_9_x86_64.whl", hash = "sha256:fb73e0011b8793c053bfa85e53129ba5f0250fdc0392c1591fd35d915ec75c46"},
+    {file = "coverage-6.4.1-cp37-cp37m-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:106c16dfe494de3193ec55cac9640dd039b66e196e4641fa8ac396181578b982"},
+    {file = "coverage-6.4.1-cp37-cp37m-manylinux_2_5_i686.manylinux1_i686.manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:87f4f3df85aa39da00fd3ec4b5abeb7407e82b68c7c5ad181308b0e2526da5d4"},
+    {file = "coverage-6.4.1-cp37-cp37m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:961e2fb0680b4f5ad63234e0bf55dfb90d302740ae9c7ed0120677a94a1590cb"},
+    {file = "coverage-6.4.1-cp37-cp37m-musllinux_1_1_aarch64.whl", hash = "sha256:cec3a0f75c8f1031825e19cd86ee787e87cf03e4fd2865c79c057092e69e3a3b"},
+    {file = "coverage-6.4.1-cp37-cp37m-musllinux_1_1_i686.whl", hash = "sha256:129cd05ba6f0d08a766d942a9ed4b29283aff7b2cccf5b7ce279d50796860bb3"},
+    {file = "coverage-6.4.1-cp37-cp37m-musllinux_1_1_x86_64.whl", hash = "sha256:bf5601c33213d3cb19d17a796f8a14a9eaa5e87629a53979a5981e3e3ae166f6"},
+    {file = "coverage-6.4.1-cp37-cp37m-win32.whl", hash = "sha256:269eaa2c20a13a5bf17558d4dc91a8d078c4fa1872f25303dddcbba3a813085e"},
+    {file = "coverage-6.4.1-cp37-cp37m-win_amd64.whl", hash = "sha256:f02cbbf8119db68455b9d763f2f8737bb7db7e43720afa07d8eb1604e5c5ae28"},
+    {file = "coverage-6.4.1-cp38-cp38-macosx_10_9_x86_64.whl", hash = "sha256:ffa9297c3a453fba4717d06df579af42ab9a28022444cae7fa605af4df612d54"},
+    {file = "coverage-6.4.1-cp38-cp38-macosx_11_0_arm64.whl", hash = "sha256:145f296d00441ca703a659e8f3eb48ae39fb083baba2d7ce4482fb2723e050d9"},
+    {file = "coverage-6.4.1-cp38-cp38-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:d67d44996140af8b84284e5e7d398e589574b376fb4de8ccd28d82ad8e3bea13"},
+    {file = "coverage-6.4.1-cp38-cp38-manylinux_2_5_i686.manylinux1_i686.manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:2bd9a6fc18aab8d2e18f89b7ff91c0f34ff4d5e0ba0b33e989b3cd4194c81fd9"},
+    {file = "coverage-6.4.1-cp38-cp38-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:3384f2a3652cef289e38100f2d037956194a837221edd520a7ee5b42d00cc605"},
+    {file = "coverage-6.4.1-cp38-cp38-musllinux_1_1_aarch64.whl", hash = "sha256:9b3e07152b4563722be523e8cd0b209e0d1a373022cfbde395ebb6575bf6790d"},
+    {file = "coverage-6.4.1-cp38-cp38-musllinux_1_1_i686.whl", hash = "sha256:1480ff858b4113db2718848d7b2d1b75bc79895a9c22e76a221b9d8d62496428"},
+    {file = "coverage-6.4.1-cp38-cp38-musllinux_1_1_x86_64.whl", hash = "sha256:865d69ae811a392f4d06bde506d531f6a28a00af36f5c8649684a9e5e4a85c83"},
+    {file = "coverage-6.4.1-cp38-cp38-win32.whl", hash = "sha256:664a47ce62fe4bef9e2d2c430306e1428ecea207ffd68649e3b942fa8ea83b0b"},
+    {file = "coverage-6.4.1-cp38-cp38-win_amd64.whl", hash = "sha256:26dff09fb0d82693ba9e6231248641d60ba606150d02ed45110f9ec26404ed1c"},
+    {file = "coverage-6.4.1-cp39-cp39-macosx_10_9_x86_64.whl", hash = "sha256:d9c80df769f5ec05ad21ea34be7458d1dc51ff1fb4b2219e77fe24edf462d6df"},
+    {file = "coverage-6.4.1-cp39-cp39-macosx_11_0_arm64.whl", hash = "sha256:39ee53946bf009788108b4dd2894bf1349b4e0ca18c2016ffa7d26ce46b8f10d"},
+    {file = "coverage-6.4.1-cp39-cp39-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:f5b66caa62922531059bc5ac04f836860412f7f88d38a476eda0a6f11d4724f4"},
+    {file = "coverage-6.4.1-cp39-cp39-manylinux_2_5_i686.manylinux1_i686.manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:fd180ed867e289964404051a958f7cccabdeed423f91a899829264bb7974d3d3"},
+    {file = "coverage-6.4.1-cp39-cp39-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:84631e81dd053e8a0d4967cedab6db94345f1c36107c71698f746cb2636c63e3"},
+    {file = "coverage-6.4.1-cp39-cp39-musllinux_1_1_aarch64.whl", hash = "sha256:8c08da0bd238f2970230c2a0d28ff0e99961598cb2e810245d7fc5afcf1254e8"},
+    {file = "coverage-6.4.1-cp39-cp39-musllinux_1_1_i686.whl", hash = "sha256:d42c549a8f41dc103a8004b9f0c433e2086add8a719da00e246e17cbe4056f72"},
+    {file = "coverage-6.4.1-cp39-cp39-musllinux_1_1_x86_64.whl", hash = "sha256:309ce4a522ed5fca432af4ebe0f32b21d6d7ccbb0f5fcc99290e71feba67c264"},
+    {file = "coverage-6.4.1-cp39-cp39-win32.whl", hash = "sha256:fdb6f7bd51c2d1714cea40718f6149ad9be6a2ee7d93b19e9f00934c0f2a74d9"},
+    {file = "coverage-6.4.1-cp39-cp39-win_amd64.whl", hash = "sha256:342d4aefd1c3e7f620a13f4fe563154d808b69cccef415415aece4c786665397"},
+    {file = "coverage-6.4.1-pp36.pp37.pp38-none-any.whl", hash = "sha256:4803e7ccf93230accb928f3a68f00ffa80a88213af98ed338a57ad021ef06815"},
+    {file = "coverage-6.4.1.tar.gz", hash = "sha256:4321f075095a096e70aff1d002030ee612b65a205a0a0f5b815280d5dc58100c"},
+]
 defusedxml = [
     {file = "defusedxml-0.7.1-py2.py3-none-any.whl", hash = "sha256:a352e7e428770286cc899e2542b6cdaedb2b4953ff269a210103ec58f6198a61"},
     {file = "defusedxml-0.7.1.tar.gz", hash = "sha256:1bb3032db185915b62d7c6209c5a8792be6a32ab2fedacc84e01b52c51aa3e69"},
@@ -590,13 +676,22 @@ pytest = [
     {file = "pytest-7.1.2-py3-none-any.whl", hash = "sha256:13d0e3ccfc2b6e26be000cb6568c832ba67ba32e719443bfe725814d3c42433c"},
     {file = "pytest-7.1.2.tar.gz", hash = "sha256:a06a0425453864a270bc45e71f783330a7428defb4230fb5e6a731fde06ecd45"},
 ]
+pytest-asyncio = [
+    {file = "pytest-asyncio-0.18.3.tar.gz", hash = "sha256:7659bdb0a9eb9c6e3ef992eef11a2b3e69697800ad02fb06374a210d85b29f91"},
+    {file = "pytest_asyncio-0.18.3-1-py3-none-any.whl", hash = "sha256:16cf40bdf2b4fb7fc8e4b82bd05ce3fbcd454cbf7b92afc445fe299dabb88213"},
+    {file = "pytest_asyncio-0.18.3-py3-none-any.whl", hash = "sha256:8fafa6c52161addfd41ee7ab35f11836c5a16ec208f93ee388f752bea3493a84"},
+]
+pytest-cov = [
+    {file = "pytest-cov-3.0.0.tar.gz", hash = "sha256:e7f0f5b1617d2210a2cabc266dfe2f4c75a8d32fb89eafb7ad9d06f6d076d470"},
+    {file = "pytest_cov-3.0.0-py3-none-any.whl", hash = "sha256:578d5d15ac4a25e5f961c938b85a05b09fdaae9deef3bb6de9a6e766622ca7a6"},
+]
 tomli = [
     {file = "tomli-2.0.1-py3-none-any.whl", hash = "sha256:939de3e7a6161af0c887ef91b7d41a53e7c5a1ca976325f429cb46ea9bc30ecc"},
     {file = "tomli-2.0.1.tar.gz", hash = "sha256:de526c12914f0c550d15924c62d72abc48d6fe7364aa87328337a31007fe8a4f"},
 ]
 typing-extensions = [
-    {file = "typing_extensions-4.2.0-py3-none-any.whl", hash = "sha256:6657594ee297170d19f67d55c05852a874e7eb634f4f753dbd667855e07c1708"},
-    {file = "typing_extensions-4.2.0.tar.gz", hash = "sha256:f1c24655a0da0d1b67f07e17a5e6b2a105894e6824b92096378bb3668ef02376"},
+    {file = "typing_extensions-4.3.0-py3-none-any.whl", hash = "sha256:25642c956049920a5aa49edcdd6ab1e06d7e5d467fc00e0506c44ac86fbfca02"},
+    {file = "typing_extensions-4.3.0.tar.gz", hash = "sha256:e6d2677a32f47fc7eb2795db1dd15c1f34eff616bcaf2cfb5e997f854fa1c4a6"},
 ]
 yarl = [
     {file = "yarl-1.7.2-cp310-cp310-macosx_10_9_universal2.whl", hash = "sha256:f2a8508f7350512434e41065684076f640ecce176d262a7d54f0da41d99c5a95"},
diff --git a/pyproject.toml b/pyproject.toml
index aa07567..2490a38 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -14,9 +14,11 @@ Jinja2 = ">=3.1.2"
 [tool.poetry.dev-dependencies]
 pytest = ">=7.1.2"
 mypy = ">=0.961"
+pytest-asyncio = ">=0.18.3"
+pytest-cov = ">=3.0.0"
 
 [tool.poetry.scripts]
-"repo-autoindex" = "repo_autoindex.cmd:entrypoint"
+"repo-autoindex" = "repo_autoindex._impl.cmd:entrypoint"
 
 [tool.isort]
 profile = "black"
@@ -24,3 +26,6 @@ profile = "black"
 [build-system]
 requires = ["poetry-core>=1.0.0"]
 build-backend = "poetry.core.masonry.api"
+
+[tool.pytest.ini_options]
+asyncio_mode = "auto"
diff --git a/repo_autoindex/__init__.py b/repo_autoindex/__init__.py
index e4e075a..b472b0b 100644
--- a/repo_autoindex/__init__.py
+++ b/repo_autoindex/__init__.py
@@ -1,4 +1,4 @@
-from .api import autoindex
-from .base import Fetcher, GeneratedIndex
+from ._impl.api import autoindex
+from ._impl.base import Fetcher, GeneratedIndex
 
 __all__ = ["autoindex", "Fetcher", "GeneratedIndex"]
diff --git a/repo_autoindex/_impl/__init__.py b/repo_autoindex/_impl/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/repo_autoindex/api.py b/repo_autoindex/_impl/api.py
similarity index 100%
rename from repo_autoindex/api.py
rename to repo_autoindex/_impl/api.py
diff --git a/repo_autoindex/base.py b/repo_autoindex/_impl/base.py
similarity index 100%
rename from repo_autoindex/base.py
rename to repo_autoindex/_impl/base.py
diff --git a/repo_autoindex/cmd.py b/repo_autoindex/_impl/cmd.py
similarity index 100%
rename from repo_autoindex/cmd.py
rename to repo_autoindex/_impl/cmd.py
diff --git a/repo_autoindex/template.py b/repo_autoindex/_impl/template.py
similarity index 100%
rename from repo_autoindex/template.py
rename to repo_autoindex/_impl/template.py
diff --git a/repo_autoindex/tree.py b/repo_autoindex/_impl/tree.py
similarity index 100%
rename from repo_autoindex/tree.py
rename to repo_autoindex/_impl/tree.py
diff --git a/repo_autoindex/yum.py b/repo_autoindex/_impl/yum.py
similarity index 100%
rename from repo_autoindex/yum.py
rename to repo_autoindex/_impl/yum.py
diff --git a/tests/test_noop.py b/tests/test_noop.py
new file mode 100644
index 0000000..6654d40
--- /dev/null
+++ b/tests/test_noop.py
@@ -0,0 +1,37 @@
+import pytest
+
+from repo_autoindex import autoindex
+
+
+async def fetcher_none(url: str) -> None:
+    return None
+
+
+async def fetcher_error(url: str) -> None:
+    raise RuntimeError("simulated error")
+
+
+async def test_no_repo():
+    """If Fetcher finds no content, autoindex should gracefully produce nothing."""
+
+    entries = []
+    async for entry in autoindex("https://example.com", fetcher=fetcher_none):
+        entries.append(entry)
+
+    # It should not have generated any index, nor raised an error,
+    # since the fetcher returned None.
+    assert not entries
+
+
+async def test_error():
+    """If Fetcher raises an exception, it should propagate."""
+
+    entries = []
+
+    # It should raise an error
+    with pytest.raises(RuntimeError, match="simulated error"):
+        async for entry in autoindex("https://example.com", fetcher=fetcher_error):
+            entries.append(entry)
+
+    # It should not have generated any index
+    assert not entries
diff --git a/tox.ini b/tox.ini
index 8ef214e..a97006c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,7 +8,7 @@ deps = poetry
 skip_install = True
 commands =
     poetry install -v
-    py.test -v {posargs}
+    poetry run py.test -v --cov repo_autoindex --cov-report html {posargs}
 
 [testenv:mypy]
 commands =